Equipment with moving parts, such as rotating or reciprocating compressors, are generally provided with lubrication systems. Such lubrication systems typically comprise a pump that circulates lubricant through the equipment, and a filter that removes impurities that accumulate in the lubricant. When such equipment is to be continuously operated, the lubrication system must be particularly reliable and, to that end, often includes dual filters. When dual filters are used, one is typically on-line while the other is off-line. The on-line filter provides service to the equipment by filtering lubricant for the equipment, while the off-line filter is available for service if needed, or may be cleaned or replaced as necessary.
Dual filters are typically interconnected between the equipment and the pump through a network of lines and valves which control which filter is on-line and which filter is off-line. As shown in FIG. 1, depicting the prior art, this may be achieved by a system 10 comprising conventional dual filters 12 and 14 interconnected via lines 16 and 18 to output ports 24a and 24b of a first three-way valve 24, and via lines 20 and 22 to input ports 26a and 26b of a second three-way valve 26. The valves 24 and 26 include input and output ports 24c and 26c, respectively, and valve stems 24d and 26d, respectively, operable for controlling flow through the respective output and input ports of the valves. A pump 30 and reciprocating compressor 32 are serially connected between the input port 24c and the output port 26c, and a rupture disc 34 is connected in parallel across the pump 30. The pump 30 circulates lubricant through the first valve 24, one of the filters 12 and 14, the second valve 26, and the compressor 32. In operation, the valves 24 and 26 must both be synchronized for directing fluid, such as a gas, liquid, slurry, or the like, to flow through either filter 12 or filter 14 as the on-line filter. It can be appreciated that when the filters 12 and 14 are switched between being on-line and off-line, the valves 24 and 26 must be turned simultaneously and synchronously or the system will be blocked ("dead-headed"). As a consequence, pressure will build up and pop the rupture disc 34, causing the system 10 to lose pressure. The compressor 32 would then not receive lubrication until the rupture disc 34 was replaced, thereby necessitating a shut down of the compressor 32 before it overheated and failed, resulting in substantial down-time costs.
Therefore, what is needed is a system and method wherein filters or subsystems thereof may switched between being on-line and off-line without incurring the risk that the system will be blocked and necessitate a shut-down of the system.